more than 60 parts per million of dissolved minerals is considered to be hard water. a 750 G sample of water was found to contain .04 gram of minerals. would this sample of water be considered hard water? explain your answer.

Achemical reaction (also known as a chemical change) produces substances that are chemically different from the starting materials. an example of a chemical reaction is the formation of water from hydrogen and oxygen gas.in a physical change, a substance changes its physical appearance but not its chemical identity. an example of physical change is the formation of liquid water from solid water, a familiar process called melting. physically, liquid water looks very different from solid water (ice) but the chemical identity, water, is the same for both. which of following changes that affect the composition of our atmosphere involve physical changes and which involve chemical reactions? oxygen gas changes to ozone during thunderstorms carbon dioxide is produced by the combustion of gasoline in an automobile engine. when coal, oil, and natural gas are decomposed in landsills they produce methane gas. freezing rain develops when a warm air mass overrides a cold air mass. fog forms from water vapor when the temperature drops below the dew point

Can someone me with questions 15 to 17 plz.

What are scientists who study fossils called? ( a ) astronomers. ( b ) biologists. ( c ) geologists. ( d ) paleontologists.